Paclobutrazol Soaked Marigold, Geranium, and Tomato Seeds Produce Short Seedlings

Abstract

<jats:p>Bedding plants and many vegetable crop seeds are often sown in plug trays. Some crops, like marigold (<jats:italic>Tagetes</jats:italic> sp. L.), tend to stretch early after germination, especially if grown in low light environments. By the time growers apply plant growth regulators (PGRs), stretching of the hypocotyl has already occurred and seedling applications are ineffective. Seedling height may be controlled by applying the plant growth regulator directly to the seed. Seeds of `Bonanza Gold' marigold (<jats:italic>Tagetes patula</jats:italic> L.), `Cherry Orbit' geranium (<jats:italic>Pelargonium</jats:italic> <jats:sub>{<jats:italic>XtimesX</jats:italic>}</jats:sub><jats:italic>hortorum</jats:italic> L.H. Bailey), and `Sun 6108' tomato (<jats:italic>Lycopersicon esculentum</jats:italic> Mill.) were soaked for 6, 16, or 24 hours in paclobutrazol solutions of 0, 500, or 1000 mg·L<jats:sup>-1</jats:sup>. After the soak treatment, seeds were dried for 24 hours prior to laboratory germination testing or sowing in plug trays. Percentage of emergence and seedling height were measured 16, 26, and 36 days after sowing. Laboratory germination of treated seeds was less than that of the control, which was attributed to the PGR being concentrated around the seed on the blotters. In contrast, seedling survival was unaffected in plugs. The higher concentration of PGR and longer times of soaking increased growth regulation, but also inhibited emergence of geraniums (71% vs. 99%). When seeds were imbibed 6, 16, or 24 hours, growth restriction was 31%, 31%, and 40%, respectively, for tomato, 61%, 37%, and 76%, respectively, for geranium and 30%, 38%, and 41%, respectively, for marigold. These results indicate that PGR application to geranium, marigold, and tomato seeds may be feasible using a 6- or 16-hour soak in 500 mg·L<jats:sup>-1</jats:sup> paclobutrazol. Chemical name used: (±)-(<jats:italic>R</jats:italic><jats:sup>*</jats:sup>,<jats:italic>R</jats:italic><jats:sup>*</jats:sup>)-ß-[(4-chlorophenyl)methyl]-<jats:sub>{XsalphaX}</jats:sub>-(1,1-dimethyl)-1<jats:italic>H</jats:italic>-1,2,4-triazole-1-ethanol (paclobutrazol).</jats:p>

Tomato Early Seedling Height Control Using a Paclobutrazol Seed Soak

“…They speculated that PB adhered to the seedcoat was released into the blotter paper reaching concentrations which inhibited germination. While Pasian and Bennett (2001) found that germination in the lab was inhibited as PB concentration and soaking time increased, in the current study, neither PB concentration nor soaking time affected germination of 'Better Boy' tomato. This is similar to the findings of Groot and Karssen (1987) and Still and Pill (2003).…”

“…They concluded that in this species, newly synthesized GAs are responsible for germination. In tomato, Pasian and Bennett (2001) found that 500 to 1000 mg PB/L inhibited germination when seeds were germinated on blotter paper. They speculated that PB adhered to the seedcoat was released into the blotter paper reaching concentrations which inhibited germination.…”

“…Therefore, endogenous (preexisting) GA in the embryo and endosperm is available for germination. In addition, Pasian and Bennett (2001) reported that PB seed soak for 6 and 16 h had no effect on the percentage of usable seedlings but when seeds were soaked for 24 h the percentage decreased. In the current study, soaking up to 12 h had no negative effect on emergence.…”

“…PB absorption through the roots is very effective, moving to young shoots acropetally with translocation primarily through the xylem. Pasian and Bennett (2001) soaked seeds of Tagetes patula 'Bonanza Gold' and Pelargonium spp. 'Cherry Orbit' in solutions of PB at 0, 500, or 1000 mg·L -1 a.i for 6, 16, or 24 h. They found that increasing the PB concentration decreased germination and speculated that this was due to the diffusion of PB into the seed during imbibition inhibiting germination.…”

Drought and drought with triazoles induced changes on pigment composition and biochemical constituents of Zea mays L. (Maize)

“…The systemic properties of paclobutrazol and other triazoles have been shown to allow the application of growth retardants to seeds with either minimal or no effect on seed germination (Pasian and Bennett, 2001). Triazoles inhibit monooxygenases, which oxidase in three steps ent-kaurene to ent-kaurenoic acid, an early reaction in GA biosynthesis (Rademacher, 2000).…”